The invention is a method for manufacturing a pressure transducer in accordance with the preamble to claim 1 and the invention is furthermore a pressure transducer in accordance with the preamble to claim 7.
A pressure transducer comprising the features of the preamble to claim 6 is known. The known pressure transducer provides to downstream display, control, or regulating devices an electrical output signal in the form of an output signal voltage or output signal current that is a measure of the pressure measured. For this purpose the pressure transducer comprises a pressure sensor that can constitute, e.g., a piezo-sensor that uses the piezo-resistive effect or a thin-film pressure sensor having thin-film measurement strips. The pressure sensor is supplied using electrical auxiliary energy in that an electrical voltage is applied to it and it is subjected directly or indirectly to the pressure of a measured medium. The electrical output signal from the pressure sensor changes depending on the effective pressure, the signal being forwarded to a circuit arrangement that, e.g., comprises a bridge circuit and/or adjustable resistances for null measurement, temperature compensation and setting nominal sensitivity. The circuit arrangement is electrically connected to an interface module that generally comprises an apparatus plug into which a signal cable can be plugged for forwarding the output signal from the pressure transducer. However, the interface module can also be a cable. The known pressure transducer comprises a pressure connection, generally a component provided with an external thread, by means of which the pressure transducer can be connected--directly or by means of an adapter--to the system with the measured medium. The pressure connection is also the carrier for the pressure sensor, which is attached at the pressure connection. A tube-shaped housing, made of metal (as is the pressure connection) comprises a first and a second end section. The first end section is welded securely to the pressure connection. The circuit arrangement and any pressure sensor elements projecting from the pressure connection are arranged protected in the interior of the housing.
In the known pressure transducer, a threaded ring, made of metal and having external threads, is welded to the second end section of the housing, the section facing away from the pressure connection. Inserted into the threaded ring is the interface module and a sealing ring. A union nut, screwed onto the threaded ring and engaged with the interface module, securely attaches the interface module to the threaded ring and therefore to the housing. In order to be able to measure relative pressures, the known pressure transducer generally comprises a ventilation apparatus, which is formed in the interface module and/or in the threaded ring. Alternatively, if the interface module is a cable, ventilation can also be performed by means of an internally ventilated signal cable.
Also known is a pressure transducer that is very similar to the pressure transducer described in the foregoing, but that differs from it in that the interface module is not connected to the housing via a threaded ring welded to the housing and via a union nut, but rather is connected to the housing directly by means of flanging and pressing the second end section of the housing.
In the course of manufacturing the known pressure transducer as described in the foregoing, the pressure connection, pressure sensor, and circuit arrangement are connected mechanically and electrically to form a sub-system. The threaded ring is welded to the housing. Then the interface module is inserted into the threaded ring and secured to it by means of the union nut. It is not until this point that the interface module is placed in electrical contact with the circuit arrangement and the housing is placed on the pressure connection of the sub-system and contact welded to it along the circumference of the first end section of the housing. The pressure transducer assembled in this manner then undergoes functional testing and is adjusted. This includes subjecting it to various temperatures so that it can be determined whether the desired display accuracy has been achieved for the ranges of permissible ambient temperature and whether the measured medium is at the permissible temperature so that any required adjustments can be made.
Since in the known procedure functional testing and adjustments must be performed on the fully-assembled pressure transducer, access to the interior of the transducer is necessarily difficult and making adjustments is a relatively complicated procedure.
Numerous different types and sorts of apparatus plugs are known and in use. This has led to a situation in which various versions of a particular type of pressure transducer are produced, and these differ from each other in terms of interface module (namely, the type of apparatus plug) and in terms of housing shape adapted to the interface module, but they are otherwise identical. To the pressure transducer manufacturer this means that the manufacturer must maintain in storage various versions of the same type of pressure transducer if the manufacturer wants to be able to fill short-notice orders from customers. In particular, the costs of the complex storage required for this can be reduced in that the manufacturer does not perform final assembly i.e., assembly of the sub-system comprising pressure connection, pressure sensor, and circuit arrangement with the housing and interface module until after a customer has placed an order. However, this increases delivery time by the time required for this final assembly and for the functional testing and adjustments that cannot be performed until after the housing has been attached to the pressure connection.
The object of the invention is to develop the method in accordance with the preamble to claim 1 such that the disadvantages described in the foregoing are avoided. This includes making it easier to make adjustments and perform functional testing. Another aspect that is an improvement is that a plurality of different interface modules will be selectable for one and the same type of pressure transducer without this resulting in expensive storage arrangements or lengthy delivery times.
Furthermore, the object of the invention is to develop the pressure transducer in accordance with the preamble to claim 6 such that its manufacture is simplified. In particular, the pressure transducer created should be suitable for manufacture in accordance with the invented method.
The object stated is achieved in terms of method by the method in accordance with claim 1. Provided in accordance with the invented method, the housing is attached at the pressure connection of the sub-system prior to the interface module being electrically connected to the circuit arrangement and mechanically connected to the housing. While for the conventional method the interior of the pressure transducer is difficult to access after connecting the housing to the sub-system due to the interface module being connected to the housing beforehand, in the case of the invention, after the housing is attached to the pressure connection, the housing is still open at its second end section so that the interior of the pressure transducer is easier to access and is thus easier to adjust.
The ability provided by the invention to perform functional testing and adjustments prior to the interface module being mechanically connected to the housing and placed in electrical contact with the circuit arrangement furthermore has the advantage that no additional adjustments or functional testing are necessary after the interface module is connected to the housing. If a certain type of pressure transducer is optionally to be provided with a plurality of different interface modules, this can be done such that only the different selectable interface modules are maintained in storage and such that final assembly, i.e., assembling the interface module with the housing, is not done until a customer has placed an order. Delivery time is still short because functional testing and adjustments have already been performed prior to this assembly. In addition, the expenses associated with storage are reduced because only various interface modules (and not pre-manufactured sub-systems made of housing and interface module) are pre-manufactured and stored when, as is advantageously provided, the housing is designed such that it can be connected to each of the different interface modules.
With regard to the pressure transducer, the object upon which it is based is achieved by the pressure transducer in accordance with claim 7. In this claim it is inventively provided that the connection between the interface module and the second end section comprises a locking apparatus.
In this context a locking apparatus is a connecting apparatus in which the two parts connected to each other move relative to each other while connected until a projection in one of the two parts locks into a seat in the other of the two parts. Such a locking apparatus can be realized by means of a so-called "snap" apparatus in which the projection in elastically deformed during the joining process until it can expand into the seat and thereby lock in it. However, the locking apparatus can also be realized by means of a bayonet coupling apparatus in which a bayonet base engages at the end of an angled bayonet slot or an angled groove and is held in this position by an elastic force.
Because of the inventive design, conventional welding of a threaded ring to the second end section of the housing is no longer necessary in the pressure transducer in accordance with the invention. This simplifies manufacture of the pressure transducer in accordance with the invention.
In an advantageous design of the invention it can be provided that the second end section of the housing is cylindrical in shape, that a locking ring engages the cylindrical end section, that the locking apparatus comprises at least one projection, which is located either on the locking ring or on the cylindrical end section, and furthermore comprises at least one seat, which is located on the other of these two parts (cylindrical end section or locking ring) and into which the projection locks, and that the interface module is connected to the locking ring. In this design, manufacture of the locking apparatus requires only a translational movement of the locking ring relative to the housing in the direction of the axis of the end section. This movement can be caused to occur using simple tools or even manually. Furthermore, affixing the locking ring does not require heat, as welding would.
If the locking ring comprises a plastic, as is advantageously provided, manufacture of the locking ring itself is simplified in comparison to manufacture of the metal threaded ring in the conventional pressure transducer.
In an advantageous design of the invention, furthermore, it can be provided that the locking ring is positioned on the external side of the cylindrical end section, that the locking ring is provided with external threads on its external side, that the interface module comprises an annular flange, and that a union nut is threaded onto the external threads of the locking ring and holds the annular flange in place on the locking ring. Essentially the same parts can be used in this design as in the conventional pressure transducer; however, the deciding advantage is that the welded connection has been replaced with the locking apparatus using the locking ring.
As an alternative to the preceding design, in an advantageous design of the invention it can be provided that the locking ring and interface module are connected to form a sub-system so that then the union nut is not required and the entire approach to the mechanical connection between the interface module and the end section of the housing is reduced to locking on the sub-system that comprises the interface module and locking ring.
Furthermore, in an advantageous design it can be provided that there is a recess on the side of the locking ring facing the cylindrical end section and/or on the side of the cylindrical end section facing the locking ring, that in the region of the recess both the cylindrical end section and the locking ring are provided an opening, and that arranged in the recess is a membrane made of a material that is liquid-impermeable and gas-permeable. This creates a simple and reliable ventilation apparatus.
Further designs of the invention are characterized in subordinate claims.
Exemplary embodiments of the invention are illustrated in the drawings and explained in greater detail in the following.